As the number of diabetic patients increases globally, the demand for insulin pumps is also increasing. An insulin pump needs to inject insulin at a low dosage at a constant rate or a large dosage according to the requirements of a diabetic patient to correct high blood sugar after a meal is eaten. The insulin pump can inject insulin according to a basic dosage distribution diagram of the diabetic patient, and therefore, the blood sugar concentration in the blood of the patient can be kept at the same level, and organs of the patient bear less pressure. Accordingly, the insulin pump must be capable of injecting insulin at a small dosage (about 0.1-1.0 cm3/day) continuously, and be capable of adjusting the speed of injection (that is, the basic dosage speed and the large dosage speed) in a wide range, to meet different requirements of patients. As a result, many insulin pumps available in the market are mini lead screw pumps; the mini lead screw pump drives a sleeve to move within a reservoir, to input the insulin inside the reservoir into the body of the patient. A motor for rotating the lead screw may be a stepper motor that can control the rotation speed precisely. On one hand, using the stepper motor increases the price of the insulin pump, the price of this type of insulin pump may be up to 5000 dollars, which greatly limits the use by patients. On the other hand, the precision of the stepper motor controlling the infusion speed depends on the number of phases and the number of beats, and the more the number of phases and the number of beats are, the higher the precision is. Low-frequency vibration easily occurs when the stepper motor rotates at a low speed. Step loss or locked rotor easily occurs at an over-high start-up frequency or overly high load, and overshoot may occur if the rotation speed is too high when the motor stops. In order to reduce the price of the insulin pump, the present invention uses a magnetoresistive angle sensor and a DC motor together to replace the stepper motor, thereby reducing the cost of the insulin pump, and improving the performance of the insulin pump.